1. Field of the Invention
This invention relates to the structure of a flexible article comprising a rubberlike flexible body having a hard film on the surface thereof such as, for example, a hose, a handrail a belt or a diaphragm, improvements in eliminating the undesirable phenomenon of "joint cracking", i.e., the development or propagation of cracks into the rubberlike body when the hard surface film is cracked for an impact.
2. Description of the Prior Art
In order to improve the wear resistance, reduction in friction factor and barrier effect against liquids (such as gasoline, light oil, alcohol-mixed gasoline), and gases (such as natural gas, liquefied petroleum gas, Freon gas) of soft rubber articles including fluidtransporting hoses, handrail bodies for use in escalators and automatic lines, and belt bodies for use in various machines, the surface of the rubber articles is conventionally hardened by ebonite formation, lining with cured films and painting while maintaining the flexibility of the whole rubber bodies.
However, if the hardness at the surface alone is increased, "joint cracking phenomenon" which may cause problems in the rubberlike bodies. An example is shown in FIG. 1, with reference to a rubber hose for use in automobile brakes. If small crack 3 occurs as shown in FIG. 1(a) by a shock in a hard and thin surface film (plastic film) 2 provided at the inner periphery of a rubber hose body 1, it develops in a short time to a deep and big crack 4 reaching the rubberlike body as shown in FIG. 1(b) by later deformation and repetition of shock and deformation. In addition, since hard plastic films have deformation fatigue values smaller than those of soft rubber, surface fatigue cracks sometimes become the nuclei to cause joint cracking. Therefore, it was difficult to provide a cured layer at the surface alone in flexible articles including handrails and belts as well as the said rubber hose which may receive large deformation and repetition of deformation.
The flexible articles including hoses, handrails and belts are generally embellished by use of color rubber (decorative rubber) or paints at the most outer layer. However, the flexible articles of such a structure have poor embellishment endurance and cleaning resistance. In terms of embellishment endurance, color rubber which is soft and is contaminated and swells with fat and oil has poor embellishment endurance. It is also difficult with paints to maintain long the beauty of the surface because of peeling and contamination of the paint layer. Also, fatigue cracking easily occurs in the hard films. In terms of cleaning resistance, it is difficult to wash and clean rubber and paints with a strong detergent and a solvent, since they easily wear by hard rubbing with a brush and the like, loosing surface smoothness and gloss, and sometimes being affected by organic solvents and detergents. Also, if the most outer layer is a colored cloth, it easily becomes dirty and hardly cleans.